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1000w halogen bulb to led - maths help needed

Matt Rozier

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Hi everyone, I’ve been using a 1000w tungsten bulb in a chimera pancake for a while - but I’m finding the noise issue when dimming is becoming more of a problem and the need for a daylight option starting to mount. 

I’m wondering what Led would be a good replacement and can’t figure out how much power I need? 

On my 1k bare bulb I’m getting around 200 fc or at 1m - so a light that gives off around 2000 Lux @ 1m might do the job, not too difficult thing to find. 
But I’m thinking, LED is quite directional, whereas a triolet bulb is shooting out light everywhere. Is there anyway I can calculate an equivalency so I can find something that might be a rough match? 

It may be that the more experienced of you out there might have a better idea?  

Im wondering if I can replace the tungsten bulb with something like a Godox sz150r which has a 120 degree beam angle and around 4500 Lux bare bulb @ 1m.  That’d just give me a lot more flexibility. 

Any advice? 

Edited by Matt Rozier
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This is quite difficult to work out accurately, mainly, as you suggest, because the radiation pattern of LEDs and tungsten-halogen bulbs isn't the same. The measurement in lux you state is a point measurement, so if your LED is only emitting into a narrow beam, the total amount of light might not be that large.

As a practical matter, things like the Godox you mention tend, without the reflector, to have something a bit less than a 180-degree radiation pattern. This tends to do quite well if you can mount it in the right point relative to the chimera's diffuser; you're just not bouncing it off the internal reflective surfaces. You may need to do some minor mechanical engineering to ensure it is in the right place relative to the diffuser. I think Aputure have some diffusers and softboxes that are designed to go on their lights, anyway.

As a matter of power level, the 150W LED is unlikely to produce the same amount of light in total as the tungsten halogen. The advantage of LED over tungsten is perhaps 5:1, so your 150W light might equate to a 750W tungsten, but the differences in radiation pattern make that a false equivalence. Given that bouncing most of the light off the chimera's reflector is a lossy process that you may not need with the LED, you may find it does quite well. If you wanted daylight, gelling your existing tungsten is a very lossy process, and a 150W daylight LED should easily outperform gelled tungsten.

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Phil that’s exactly what I need. 

It’s been a real head scratcher - I def know I’ll be giving up a bit of level, I suppose I’m just trying to figure out how much I’d be sacrificing in terms of level in order to gain a lot more in terms of flexibility.  There’s definitely more powerful led units out there - just that one seems to tick a fair few boxes so gives me a little more bang for the buck. 

But I’m glad I asked for help as I’d still be scratching head and no closer to an answer lol. 

Thanks so much for your help- really appreciated! 

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  • 1 month later...

I have two Mole Richardson 407 1k fixtures that I've put Visionsmith LED relamps in. It's still a little weird grabbing them when they're on but they work well and the 407 has a decent size Fresnel lens on it. The daylights run around 5200k in temperature FYI and aren't quite 1k in power but work very well and the fans are very quiet. I'll also add that Moles are very fast and easy to adjust compared to most other lights. 

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